Exhaust Gas Temperature (EGT) and fuel flow of an engine are used by a pilot of an aircraft during cruise flight to conserve fuel and extend range. The pilot monitors the temperature of the exhaust gas output from cylinders in the engine while adjusting fuel flow.
For best power, the pilot uses the first cylinder to reach a peak EGT when reducing fuel flow (the leanest cylinder) as a reference. Having determined the first cylinder to reach a peak EGT, the pilot increases fuel flow until the EGT in that cylinder decreases to within a predefined range of the detected first cylinder peak (rich of peak).
Automated systems to aid the pilot in achieving best power are available. One such automated system is JP Instrument's Engine Data Management 900 (EDM-900). The EDM-900 automatically detects the first cylinder to reach a peak EGT when leaning and displays the peak EGT on the display allowing the pilot to monitor the decrease in EGT while increasing fuel flow.
For best economy, the pilot continues to reduce fuel flow and monitor the EGTs of the other cylinders until the last cylinder reaches a peak EGT. The pilot continues to reduce the fuel flow until the EGT of the last cylinder to reach a peak EGT decreases to within a predefined range of the last cylinder's peak EGT (lean of peak).
This complicated process (known as engine fuel mixture leaning) requires monitoring exhaust gas temperatures and computing lean and rich of peak values and must be recomputed each time there is a change in altitude or power lever position. Thus, due to the complicated procedure many pilots do not lean the fuel flow mixture to the respective aircraft engine resulting in use of more fuel than necessary. Other pilots decide on an arbitrary power setting with no attempt to achieve best power of the aircraft engine.